Kalispell, MT planting calendar
- USDA zone
- 5b−15 to −10 °F
- Last frost
- May 31avg, 32°F
- First frost
- Sep 10avg, 32°F
- Growing season
- 100days
Kalispell, Montana is in USDA plant hardiness zone 5b. Its average last spring frost is around May 31 and the first fall frost around September 10, giving a growing season of about 100 days (NOAA 1991–2020 normals, 32°F, median). Start tender crops like tomatoes and peppers indoors weeks before the last frost and set them out afterward; sow hardy crops such as peas, spinach, and lettuce before it. The planner below turns those frost dates into a printable per-crop planting calendar.
Kalispell planting calendar
Each crop's windows are counted from Kalispell's average frost dates. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees.
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting |
|---|---|---|---|---|---|
| Tomato | Tender | Apr 5 – Apr 19 | Jun 7 – Jun 14 | Aug 6 – Aug 26 | — |
| Pepper | Very tender | Mar 22 – Apr 5 | Jun 14 – Jun 21 | Aug 13 – Sep 12 | — |
| Cucumber | Tender | May 3 – May 10 | Jun 7 – Jun 14 | Jul 27 – Aug 16 | — |
| Summer squash / zucchini | Tender | — | Jun 7 – Jun 14 | Jul 22 – Aug 6 | — |
| Bush bean | Tender | — | Jun 7 – Jun 14 | Jul 27 – Aug 6 | Jul 12 – Jul 22 |
| Sweet corn | Tender | — | May 31 – Jun 14 | Jul 30 – Aug 29 | — |
| Basil | Very tender | Apr 19 – May 3 | Jun 7 – Jun 14 | Jul 7 – Jul 22 | — |
| Lettuce | Half-hardy | Apr 19 – May 3 | May 3 – May 17 | Jun 17 – Jul 2 | Jun 28 – Jul 13 |
| Pea | Hardy | — | Apr 19 – May 3 | Jun 13 – Jun 28 | Jun 18 – Jul 3 |
| Spinach | Hardy | — | Apr 19 – May 3 | May 29 – Jun 8 | Jul 8 – Jul 18 |
| Carrot | Half-hardy | — | May 10 – May 17 | Jul 9 – Jul 29 | Jun 8 – Jun 28 |
| Broccoli | Half-hardy | Apr 5 – Apr 19 | May 3 – May 17 | Jun 27 – Jul 17 | Jun 13 – Jul 3 |
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Frost & freeze dates
From NOAA's 1991–2020 Climate Normals at station USC00244558. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 (p10 for spring, p90 for fall) — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | — | — | — | — | 60 |
| 32°F (freeze) | May 31 | Jun 22 | Sep 10 | Sep 25 | 100 |
| 28°F | May 10 | May 26 | Sep 27 | Oct 7 | 136 |
| 24°F | Apr 28 | May 11 | Oct 6 | Oct 21 | 162 |
32°F is the standard "freeze" line that damages tender crops; lighter 36°F frost can nip the most cold-sensitive plants, while hardy crops shrug off light frost down toward 28°F. Use the threshold that matches what you are protecting.
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. Warm-season crops need a long, warm GDD total; a short, cool GDD total favors greens and brassicas.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 1,425 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,106 | cool-season crops (brassicas, greens) |
Hardiness zone 5b
Kalispell sits in USDA plant hardiness zone 5b on the 2023 map — meaning its average annual extreme minimum winter temperature is about −15 to −10 °F. That number tells you which perennials, shrubs, and trees reliably survive an average winter here; it does not set your planting dates, which come from the frost calendar above.
Explore more places in zone 5b, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Kalispell?
- Kalispell, Montana is in USDA plant hardiness zone 5b on the 2023 map (average annual extreme minimum temperature −15 to −10 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.
- When is the last frost in Kalispell?
- The average (median) last spring frost at 32°F is around May 31, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as June 22, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Kalispell?
- The average first fall frost at 32°F is around September 10. That leaves a growing season of about 100 days between the average last spring and first fall frosts.
- When should I start tomatoes in Kalispell?
- Start tomato seeds indoors about Apr 5 – Apr 19 and transplant them outside about Jun 7 – Jun 14, once the danger of frost has passed. Estimated first harvest is around Aug 6 – Aug 26.
- How long is the growing season in Kalispell?
- About 100 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 31) and the average first fall frost (~September 10). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020 for station USC00244558 (Kalispell Glacier Ap, 13.2 km away). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.